Copy machines, printers and similar image forming devices that use scanning laser beams generally include laser scanning optical systems. A laser scanning optical system may use light from a laser beam light source that passes through a collimating lens in order to provide collimated light that is transformed to lines by a cylindrical lens. The light is then reflected from a rotary polygon mirror through an fxc2x7xcex8 lens to an image plane. Reflective mirrors are used to fold the light path between the laser and the image plane. The various optical elements are mounted in fixed positions on a housing that may, for example, be made of synthetic resin.
FIG. 6 shows a conventional lens supporting structure for a lens holder for a lens, such as a collimating lens. As shown in FIG. 6, lens 70 is held in place by positioning the lens holder 71, that holds the lens 70, in a V-shaped recess 61a of a mounting structure 61 that is integrally molded to form part of the housing 60. Lens holder 71 is held down elastically with a U-shaped plate spring 62 that is screwed on upper end surfaces of the mounting structure 61 that are on opposite sides of the lens holder 71. The lens holder 71 is held in contact with surfaces of the V-shaped recess 61a. That general arrangement is also disclosed in Japanese Laid-Open Patent Application H06-160745. In that application, the lens holder is inserted and fitted into a U-shaped recess of a housing and held by a plate spring. However, the elastic force of the plate spring may become less with time and allow undesired rotation of the lens holder about the optical axis of the lens that is held in the lens holder. Japanese Laid-Open Patent Application H05-11202 discloses a similar arrangement with a lens holder held by a plate spring in a U-shaped recess of a housing. That application discloses that adhesive may be used to prevent rotation of the lens holder. However, the use of adhesive prevents easy removal of the lens housing and increases the materials and the manufacturing steps required, thereby increasing production costs.
To avoid some of the problems of the embodiments of the two applications just discussed, an alternative known construction of a lens supporting structure, as shown in FIG. 7, uses flanges 71a on opposite sides of the lens holder 71. These flanges are screwed into the upper end surfaces of the recess 61a of the mounting structure 61 that is integrally molded to form part of the housing 60. To fix the position of the lens holder, as shown in FIG. 7, one of the flanges 71a is tightly screwed to one upper end surface of the recess 61a of the mounting structure 61 in order to bold the lens holder 71 in contact with surfaces of the recess 61a. However, as shown in FIG. 7, the other flange 71a may not be held in contact with the other upper end surface of the recess 61a due to dimensional tolerances and other variations during manufacture. Therefore, in many cases, the connection to the mounting structure 61 at the second flange may be weaker than intended and also may not provide the desired stability to the lens holder 71 and the lens 70.
The undesirable optical effects of instability of the lens holder may be especially severe when the lens holder is holding a cylindrical lens, which optical systems, including laser beam scanning optical systems, often include. As shown in FIG. 8, vertical positioning of the lens holder with tight contact of both flanges 71a of the lens holder 71 with the upper end surfaces of the recess 61a may be achieved by leaving a gap between the lens holder and the surfaces of the recess 61a. However, that arrangement provides less stability of the lens holder in the other direction perpendicular to the optical axis. That instability is especially undesirable when the lens holder is holding a collimating lens, which optical systems, including laser beam scanning optical systems, often include. In either the FIG. 7 or FIG. 8 prior art embodiments, it is impossible to establish a light path with high accuracy because the optical axis of a lens held in the lens holder cannot be reliably aligned.
The present invention relates to a lens supporting structure of inexpensive construction that fixes a lens onto a housing with high accuracy and stability. The lens holding structure of the present invention may be used in laser scanning optical systems, including those used in copiers and printers.